Liposome is an artificial membrane, when the amphiphilic molecules such as phospholipids and sphingolipids are dispersed in the aqueous phase, the hydrophobic tails of the molecules tend to aggregate together to prevent away from the aqueous phase, while the hydrophilic heads expose to the aqueous phase, phospholipids in water spontaneously form molecular organized assemblies relying on hydrophobic interaction, and form a bilayer structure of closed vesicles. Liposomes consist of a continuous bilayer or multi-layer lipid, each layer is lipid bilayer membrane, interlayer and liposome core are the aqueous phase, while the bilayer is the oil phase. Liposomes can be used as an experimental model of biomembrane, they are often used as carriers of drugs, enzymes or other agents in research and therapy, which are made more effective delivery to the target cells, and released through cell fusion.
Liposome shows many advantages, such as simple preparation, non-toxic and non-immunogenic response, in vivo degradation, easy to accomplish targeting, improving and prolonging the drug efficacy, moderating toxicity, avoiding drug resistance and changing the route of drug administration. In addition, it shows amphiphilic properties, hydrophilic and hydrophobic drugs can be both entrapped, water-soluble drugs can be loaded into the aqueous phase of the liposome, and oil-soluble drugs or amphiphilic drugs can be loaded into the lipid bilayer, so liposome has broad applicability for various drugs. Since the 1970s, liposomes have attracted much attention in the application of drug carriers.
However, liposomes have the limitation of instability which hampers its practical application. Specifically during storage, liposomes may be destroyed due to the reasons of drug leakage, aggregation of particles and oxidation or hydrolysis of phospholipids and so on. In the body, due to the interaction with blood albumin, conditioning factors, antibodies and other substances, liposomes may be ruptured, causing rapid leakage of encapsulated drugs, which are quickly degraded by some enzymes and swallowed by some phagocytic cells, and cannot effectively reach the targeted tissue to play their role. Therefore, the development of stable liposomes as drug carriers is a prerequisite for practical application, which shows great significance.
In recent years, a variety of functional liposomes have been gradually developed, such as temperature-sensitive liposomes, pH-sensitive liposomes, light-sensitive liposomes and so on, resulting in the possibility of site-fixed, time-regular, quantitative release of the drug. Among them, the light-sensitive liposome has unique advantages, when the drug is embedded in such type of material and delivered into a specific location of the body, configuration of light sensitive group can be changed simply by external light irradiation, leading to controlled release of the entrapped drug. Currently, many of the light-control materials reported are azobenzene derivatives, and introduction of azobenzene derivatives into liposome may reach the results of site-fixed, time-regular, quantitative release of drugs, but there are still some problems. For example, the use of azobenzene-containing surfactants as light-control material is prone to cause phase separation and fusion of liposome (Chem. Lett. (1981) 1001-1004), while the introduction of azobenzene containing phospholipids as light-controlled release materials will decrease the stability of liposome, lead to a sudden release of drugs, thus making it difficult for practical application (Photochem. Photobiol. 62 (1995) 24-29).
Cholesterol is an important component of cell membranes. The most important function of cholesterol is regulating physical and chemical properties of cell membrane (Yeagle P L. Biochim Biophys Acta 1985, 822 (3-4), 267-87; Yeagle P L. In: Yeagle P L, editor. Biology of cholesterol. Boca Raton (FL, USA): CRC Press, 1988. p. 121-146). In the cell membrane, cholesterol can interact with phospholipids or sphingolipids membrane and thus affect their properties. Increased levels of cholesterol in the lipid bilayer will expand and eventually eliminate coordination of the gel liquid crystal phase transition of the lipid bilayer (Lewis R N A H, McElhaney R N. In: Yegle P L, editor. The structure of biological membranes. Boca Raton (FL, USA): CRC Press, 1992. p. 73-156; Maulik P R, Shipley G G. Biophys J 1996, 70, 2256-2265). Cholesterol in the phospholipid bilayer is presented at an intermediate state, when above the phase transition temperature, the membrane fluidity is decreased, and when below the phase transition temperature, the membrane fluidity is increased (Demel R A, de Kruijff B. Biochim Biophys Acta 1976, 457 (2), 109-132). In the biologically relevant liquid crystal state, the arrangement of cholesterol in the membrane is relative ordered, so that movement rate of the alkyl chain of phospholipids decreases. In the membrane relatively ordered state, the membrane will be made more dense, thereby the mechanical properties of the membrane is increased and the permeation performance is decreased (Lund-Katz S, Laboda H M, McLean L R, Phillips M C. Biochemistry 1988, 27 (9), 3416-3423). In addition, cholesterol in organisms and traditional liposomes is generally in a free state. In the practical research and application, free cholesterol tends to quickly move out from the liposome membrane (Kan, C C; Yan, J.; Bittman, R. Biochemistry 1992, 31, 1866-1874; Hamilton, J A Curr. Opin. Lipidol. 2003, 14, 263-271), which makes the stability of liposomes decrease and severely limits the application of liposome as drug carriers.
Porphyrin and its derivatives are macrocyclic molecules containing four conjugated pyrrole rings. It has a very wide range of applications in medicine, biochemistry, analytical chemistry, synthetic chemistry, and materials science because of its unique performance and easy modification, especially porphyrin derivatives, which have unique electronic structure and optical properties. In recent years, it has attracted much attention in medicine, optical storage, molecular devices, simulation design and synthesis of artificial systems for simulating charge separation, electron transfer and signal transduction. However, porphyrin derivative is generally a rigid molecule, it is difficult to be molded, and also its water solubility is relatively poor, which to some extent limits its practical application (J. Photochem. Photobiol., B 2002, 66, 89-106). In addition, when porphyrin derivatives including metal complexes are directly applied to the organism, there are also many problems in the safety and effectiveness.
The porphyrin molecule is embedded in the micelle, liposome, low-density lipid protein, polymer micelles or hydrophilic polymers and other carriers to improve its water solubility and biocompatibility. But the micelle carrier system is often prone to elicit acute hypersensibility (anaphylactic) reactions in vivo (Br. Med. J. 1980, 280, 1353-1353), the liposome is prone to opsonization and subsequent capture by the major defense system of the body (J. Pharm. Sci. 1995, 84, 166-173), and polymer shows poor tumor regression and increased accumulation in normal tissues (J. Pharm. Pharmacol. 2001, 53, 155-166). All the above carriers have a common drawback, in which the porphyrin derivatives embedded are easy to leak out, resulting in phototoxic side effects. The carrier-embedded silica-based nanoparticles with a high degree of stability, good biocompatibility and water dispersion can overcome the above disadvantages arising from other carriers, can be easily modified with different functional groups, and are not vulnerable to microbial attack. (J. Am. Chem. Soc. 2003, 125, 7860-7865).
In addition, encapsulation efficiency is a practical measurement for liposome's application as drug carriers. There are many ways to improve the encapsulation efficiency of liposome at present (Chinese Pharmaceutical Industry 2002, 33 (11), 564-568), and the way through intermolecular interactions or electrostatic attraction to improve liposome's encapsulation efficiency has significant advantages. Among them, liposomes with benzene rings can generate intermolecular conjugation with a number of drugs with similar groups, such as camptothecin, etc., which effectively increase the drug-embedded efficiency (Journal of Controlled Release, 2008, 127, 231-238). Liposomes derived from lipid containing carboxylic groups have many free carboxyl groups on the surface. On one hand, it facilitates coupling with drugs containing hydroxyl or amino groups such as doxorubicin. On the other hand, such liposomes can take a wealth of negative charge under specific pH values, which are well suited for the entrapment of drugs through electrostatic attraction. Thus the encapsulation and drug loading efficiency can be greatly improved. Meanwhile, liposomes with rich carboxyl groups on the surface can also facilitate the modification of a variety of targeting molecules to improve their targeting effect.
Currently, most of the liposomes are prepared by phospholipid, electrostatic, hydrophobic and van der Waals interactions between these liposomes with plasma proteins, conditioning factors, antibodies and other substances, which often leads to destabilization of liposomes, which generally makes liposomes be quickly removed before reaching the target in the circulation and encapsulated drug be quickly released prior to reaching their target tissue. This not only makes the drug unable effectively to play its role, but also may cause serious side effects. In addition, the drug can interact with the phospholipid of liposome (for example, anthracycline adriamycin showed surfactant or detergent-like effects to the phospholipid bilayer), which will lead to drug leakage during storage and make the liposome more unstable. The liposomes have shortcomings such as in vivo instability and storage instability, thus limiting the clinical application and industrial production of liposome. Although research of liposome has been carried out for decades, development of liposome-drug formulations is still very few, and poor stability of liposome is a serious problem in its commercialization process. Therefore, the development of stable liposomes as drug carriers is a prerequisite to practical application, which shows great significance.
Based on the above considerations, in the present invention, the inventors designed and synthesized a new class of hybrid lipids, the molecular structure of such lipids contains —Si(OEt)3 or —Si(OCH3)3 groups. In aqueous solution such lipids can self-assemble to form vesicle structure with a lipid bilayer, and there is a stable Si—O—Si network structure on the vesicular surface and covalent bonding with the surface of the liposome, which greatly enhances its stability and water solubility.
Based on these novel hybrid lipids, the inventors have made a series of related research, for example, an azobenzene unit was introduced into the molecular structure of the novel hybrid lipids, and the lipid bilayer permeability can be easily controlled by light irradiation to achieve controlled release of drugs; cholesterol groups were covalent bonded with the novel hybrid lipids, and lipid bilayer fluidity and permeability can be further adjusted, thus formulation can effectively prevent the loss of cholesterol and can be used as a model for studying structure and function of cell membrane; benzene rings or carboxylic acid groups were bonded with new hybrid lipids, thus encapsulated hydrophobic or hydrophilic drugs can interact by conjugated effects or electrostatic attraction, thereby enhancing drug encapsulation efficiency; functional porphyrin moiety was covalent bonded with the novel hybrid lipids, which makes the porphyrin unit be orderly arranged in the bilayer structure of the formed vesicles, and then introduction of different metals through the coordination will develop a series of functional nanomaterials.